1. Field of the Invention
The present invention relates to composite bicycle wheel rims and other like wheel rims where multiple resin impregnated layers or xe2x80x9cplysxe2x80x9d of fibers are applied at selected crossing angles onto a mandrel to form a laminate, with heat and pressure applied thereto in a molding process to cure the laminate into the composite hook bead type rim that has inwardly pointing hook ends for fitting into locking grooves formed around a tire side walls.
2. Prior Art
Traditionally, wheel rims have been constructed utilizing very old stamping processes from metal, typically steel or aluminum, and while such rims are in common use, they possess several undesirable characteristics. Steel metal wheel rims corrode, and aluminum wheel rims are prone to dent and deform, and both types of rims generally offer only silver color as a finish option. Further, such stamping processes on aluminum require rolling, bending, stamping, and piercing metal, that often create micro-fractures and weakened areas of the metal that, in turn, must be heavily reinforced to create sufficient strength to endure over a predictable rim life-span. For a steel rim, while the stamping processes creates little damage to the metal, such stamping processes are very capital intensive, requiring heavy forming equipment with significant maintenance requirements. In practice, the industry recognized that a steel rim, with its excessive weight, unattractive appearance and tendency to corrosion, is not a popular item with consumers. For example, in North America and Western Europe, manufactures of steel rims are forced to operate at very low profit margins.
Presently, wheel rims constructed from a glass, carbon and graphite fibers that are attractive to consumers have generally been prohibitively expense for an average bicycle enthusiast. An example of a high quality composite rim whose construction is labor intensive and thus must be sold at a high price is shown in a U.S. Patent Application entitled xe2x80x9cA Two Component Composite Bicycle Rimxe2x80x9d, Ser. No. 09/548,068, filed Apr. 12, 200, by one of the present inventors. The present invention also provides a composite rim that is, however, formed as a more universal and less expensive bicycle rim, from inexpensive materials, preferably glass fibers, and utilizes apparatus and method for its manufacture that are more efficient and labor saving. A rim of the invention is therefore as strong as a steel rim and is as light in weight to a comparable aluminum rim, can be attractively finished, and is less expensive and accordingly has a broader sales appeal in the market place that steel or aluminum rims.
Heretofore, within the knowledge of the inventors, a composite rim like that of the invention for mounting tires formed with continuous side wall mounting grooves has not been known.
A composite bicycle rim, or like rim has heretofore usually been constructed in sections from layers or plys of unidirectional fiber layers that are laid up, one layer over another, on a mandrel, forming a laminate that is then cured under heat and pressure, with the rim sections then finished, assembled and secured together along section junctions, forming a continuous rim. The invention, in a single operation, forms a continuous unwarped composite hook bead type rim having side walls whose upper ends are formed as inwardly pointing hooks that are for fitting into side wall grooves of a molded tire, for mounting the tire onto the rim. The rim is preferably a laminate constructed by laying up, one over the other, mats or plys of resin coated or impregnated fiber glass onto a circular mandrel whose width can be reduced to pass between the rim side hook ends. The mandrel, as shown, includes movable or removable center sections that, when removed, shorten the distance across the mandrel so as to allow it, after laminate rim curing, to be conveniently removed from between the rim side wall hook ends. The hook ends are then shaped, as with a turning router blade, or the like, to extend inwardly a required distance from the rim inner side wall ends to hook into the tire side wall grooves.
To form the rim of the invention, mats or plys of resin epoxy impregnated or coated directional glass fibers are sequentially laid up, one over the another, forming a laminate, with the fiber direction of each mat or ply laid over a prior mat or ply such that the fibers are at a different crossing angles, providing a stack of fiber glass mats or plys where the crossing angles of the fibers of each mat or ply are at a selected angle to adjacent mats. So arranged, a laminate is formed having an architecture that is balanced and interlocking, providing a finished rim the is free from residual stress, without stress risers and is dimensionally stable and unwarped. In practice a stack of mats containing twenty four (24) discrete resin impregnated mats or plys of fiber glass, each of a thickness of from twenty eight (28) to thirty four (4) thousands (1000) of an inch, are laid up as a laminate on a mandrel for curing to form the rim. The twenty (24) plys are grouped in six (6) identical groups of four (4) plys each that are arranged to cross at the design crossing angles, and repeat in each of the six (6) identical groups. The first ply in a group is preferably parallel to the mold circumference, and the last ply in the group, is preferably, perpendicular to a tangent to the mold circumference, with the fibers of the center two (2) plys at crossing angles of less than ninety (90) and greater than forty five (45) degrees to one another. So arranged, after curing the laminate is remove off of the mandrel by a reduction of the mandrel cross section to allow the mandrel or mandrel sections to be slid past the inwardly pointing rim hook ends. So arranged, the rim shape will remain undeformed and faithful to the cavity of the mold.
After curing and removal from the mold, the rim hook ends as have been formed by bending the edges of the plys over the mandrel edges, are finished, as with a router. This finishing provides a required hook end distance from the rim interior side wall surfaces, and a desired spacing distance between the hook ends to allow a tire side walls to be fitted into the rim to with the hook ends passing into the tire side wall continuous grooves, mounting the tire mounting onto the rim. Prior to which tire mounting, the rim is drilled to receive spokes that radiate inwardly therefrom to fit to a hub, forming a wheel. The rim, with the drilled spoke holes, preferably receives a urethane polymer coating applied thereover that enhances the overall rim strength and finish quality, creating a smooth, colorful appearance that is unaffected by ultra-violet rays, moisture, salt-water, most chemicals, and most cleaners.
It is a principal object of the present invention to provide a continuous composite rim that is preferably formed as a laminate from inexpensive glass fiber mats or plys coated with an epoxy resin that are laid up in groups of mats or plys, with crossing angles between the plys selected to provide, a balanced laminate where the laminate, after curing, is free of stress risers and is dimensionally stable.
Another object of the present invention is to provide a composite rim that is conveniently and economically formed by laying up epoxy risen impregnated fiber mats or plys over a mandrel where upper ends of rim walls are formed as inwardly pointing hook ends by bending mat or ply along the mandrel parallel edges with, after curing in a mold, the mandrel wall to collapse, shortening its width, so as to allow the mandrel to pass between the hook ends that are each then machined to a desired distance from the surfaces of the rim interior walls to accommodate and mount to mounting grooves in a tire side walls.
Another object of the present invention is to provide a composite rim that is easy and economical to manufacture to provide a rim that is of like weight to a comparable aluminum rim and is as strong as a steel rim at lower weight than such comparable steel rim, and can be painted or otherwise colored to present an attractive appearance.
Still another object of the present invention is to provide a composite rim that, after fabrication, can be easily drilled to accommodate radially mounted spokes thereto that connect to a hub, forming a bicycle wheel.
Still another object of the present invention is to provide a rim that receives a urethane polymer coating after curing to enhance overall rim strength and finish quality, creating a smooth, colorful appearance that is unaffected by ultra-violet rays, moisture, salt-water and most chemicals and cleaners.